Loss of magmatic sulfides to the mantle is posited to explain the copper deficit of evolved arc magmas and the depleted Cu/Ag ratio of the continental crust. We address the question of whether saturating sulfides may instead be mechanically entrained with rising magmas, and how this would affect their geochemical fate in the upper crust. Entrainment is plausible considering sulfide wetting properties and settling velocities relative to magma ascent velocities. Entrained sulfide increases the pressure at which magmas become saturated with respect to H-O-S fluids in the upper crust by 10–100 MPa, with the pressure difference increasing with temperature, water content, and oxidation. Bubbles are likely to nucleate on sulfide particles, allowing transfer of S and Cu from the sulfide to the fluid over a small crystallization interval without limitations by diffusion through the silicate melt. This sequence of processes gives magmatic sulfides an active role in ore metal transport and enrichment to form porphyry copper deposits, and may have global implications for crustal Cu budgets.Porphyry copper deposits contain millions of tons of Cu enriched by orders of magnitude compared to common rocks. These extreme anomalies form by several enrichment steps from magma to fluid to ore (Sillitoe, 2010). The preceding evolution, by contrast, is currently envisioned to be a partial depletion step that is caused by sulfide saturation sequestering chalcophile metals originally present in primary arc basalts (e.g., Chen et al., 2020). A global deficit of Cu in arc volcanics above thick continental crust and in the bulk continental crust (Chiaradia, 2014), combined with common sulfide presence and partial Cu enrichment in lower crustal cumulates (Métrich et al., 1999; Rezeau and Jagoutz, 2020), is believed to indicate significant loss of Cu and other chalcophile metals by recycling to the mantle (Lee et al., 2012; Jenner, 2017; Park et al., 2021). Paradoxically, the Cu deficit of magmatic arc rocks is largest in tectonic settings that also host the world's premier porphyry copper provinces (Chiaradia, 2014; Loucks, 2021). The widespread presence of accessory sulfide in magmas associated with porphyry copper deposits indicates that sulfide saturation in the lower crust is not detrimental to ore formation (Du and Audétat, 2020; Rottier et al., 2020). The suggested roles for magmatic sulfide in the formation of porphyry copper deposits have focused on upper crustal processes; e.g., transient chalcophile element storage, sulfide accumulation and remobilization, bubble-flotation of composite particles, and wholesale or fractional sulfide decomposition upon fluid saturation, which can affect the bulk Au/Cu ratio of resulting ore deposits (Hattori and Keith, 2001; Halter et al., 2004; Nadeau et al., 2010; Wilkinson, 2013; Mungall et al., 2015; Yao and Mungall, 2020). Most recent research has instead focused on identifying tectonic and magmatic conditions that minimize lower crustal Cu loss and optimize chances of making ore deposits from the remaining Cu in evolving magmas (Richards, 2015; Lee and Tang, 2020; Rezeau and Jagoutz, 2020; Chelle-Michou and Rottier, 2021; Park et al., 2021).We question the prevailing view that sulfide saturation in the lower crust necessarily means sulfide loss and consequent metal depletion of the magma. We explore the alternative possibility that initial enrichment in magmatic sulfide is followed by mechanical entrainment of sulfide particles by ascending silicate melts (Core et al., 2006), and quantify its consequences for magmatic fluid saturation in the upper crust and the transfer of chalcophile metals to this fluid.Experiments measuring dihedral angles between mantle minerals and FeS-rich sulfide melt show that the wetting characteristics of sulfide in contact with silicate grain surfaces favor isolated sulfide spherules in silicate melt (Wang et al., 2020). Grains of monosulfide solid solution commonly forming composite spherules with more Cu- and Ni-rich sulfide melt show no tendency for preferential attachment to major oxides and silicates (e.g., Li and Audétat, 2012).Whether sulfide particles or droplets settle or remain entrained in the melt is determined by the sinking velocity of sulfide relative to the ascent velocity of the host silicate magma (Tomkins and Mavrogenes, 2003). The density difference between sulfide and silicate melt, Δr, enters linearly into Stokes' formula, whereas particle radius, r, enters by its square for a silicate melt viscosity μ:Evaluation of Equation 1 (see the Supplemental Material1) shows that the dominant compositional effects on viscosity—silica and water content—partly cancel, so that extrapolated curves for basalts approximate more fractionated melts with higher water content at lower temperature (Fig. 1). The size of sulfide particles observed as inclusions in magmatic glass and phenocrysts is typically 1–100 μm (Halter et al., 2004; Du and Audétat, 2020; Georgatou and Chiaradia, 2020), and models of sulfide particle growth by diffusion and coalescence indicate an upper limit of ~300 μm (Yao and Mungall, 2020).Ascent velocities from U-Th series disequilibria are based on transfer duration between the mantle source and the surface that include periods of storage and therefore represent minimum flow velocity (Turner and Costa, 2007). Diffusion-based speedometers yield similar estimates for lower crustal ascent and much faster velocities in the upper crust when fluid saturation initiates volcanic eruptions (Neave and Maclennan, 2020). The comparison (Fig. 1, gray bars) shows that sulfides not removed by inclusion in cumulate crystals may commonly be transported by silicate melts.Lesne et al. (2015) showed that sulfur dissolved in silicate magmas increases the pressure and depth of magmatic fluid saturation but they did not consider saturation of a separate sulfide phase, which is the focus of our analysis. We explored the relative stability of pyrrhotite, anhydrite, and a H-O-S fluid phase in equilibrium with a variably crystallized magma. The stability and decomposition of Fe-S-rich monosulfide solid solution (simplified to non-stoichiometric FeS) is controlled by reactions linking the partial pressure of gas species to H2O(m) and FeO(m) in the coexisting silicate melt. At reducing conditions, the dominant S–II species forms as (Mungall et al., 2015):and at oxidizing conditions, S+IVO2 forms as:whereby H2O(m) controls the dominant fluid species H2O(g), and O2 fugacity (fO2) is controlled by H2O(g) = 0.5O2(g) + H2(g). Intermediate-valency S2(g) and H2(g) are minor gas species, with the latter limited by H2(g) + Fe2O3(m) 2 FeO(m) + H2O(m).We evaluated these reactions by Gibbs energy minimization using the solution models from Holland et al. (2018). Compared to earlier modeling of melt-sulfide-fluid equilibria (cf. Mungall et al., 2015), the amounts of rockforming minerals in the magma vary simultaneously with the quantities of sulfide and fluid. The model chemistry is simplified compared to that of Yao and Mungall (2020) in that Cl and C are ignored, as is S solubility in the melt (a function of pressure [P], temperature [T], and melt composition, notably redox conditions; e.g., Matjuschkin et al., 2016). We disregard C because it adds an arbitrary degree of freedom to the model; calculations for plausible melt CO2 content show that while CO2 may cause fluid saturation at higher pressure, the quantity of fluid is so small that it has only second-order consequences for de-sulfidation (Fig. S1 in the Supplemental Material). Our approach is simplified but emphasizes the first-order consequence of crystallization for aqueous fluid production as a self-enhancing process because H2O loss from the melt in turn promotes crystallization. We chose the hydrous arc basalt composition of Rezeau and Jagoutz (2020), similar to that used by Chiaradia (2014) and others, which apply alternative melt models. Amphibole has been excluded because this solution model, implausibly, suppresses magnetite stability, so that pyroxenes take the place of mafic minerals in our model system (see the Supplemental Material). We present results for fixed bulk compositions, rather than cooling paths of fractional crystallization, to illustrate the effects of magmatic sulfide across a P-T region (Fig. 2). To introduce S, 0.5 wt% FeS was added to the model basalt composition. The resulting S-content is near the high end of estimates for S in primitive arc basalts compared with S solubility at sulfide saturation (Chelle-Michou and Rottier, 2021) and of petrographic estimates of sulfide abundance in sulfide-saturated mafic arc volcanics (Métrich et al., 1999; Larocque et al., 2000).At lower crustal conditions, our melt-dominated magma is fluid-free but saturated with pyrrhotite and anhydrite (which, in reality, is partly dissolved in the melt), with mafic minerals, and with + garnet ± feldspar giving way to magnetite-rich spinel + feldspar at mid-crustal pressures. Decompression causes fluid saturation (solid purple curve in Fig. 2B), the pressure of which is increased by the presence of sulfur. The magnitude of this increase, ΔP(S), was obtained by equilibrating the same bulk composition without added FeS (stippled purple curve in Fig. 2B). ΔP(S) increases with increasing temperature, which promotes de-sulfidation by Reactions (2) and (3), so that above ~1000 °C, the fluid saturation curve reverses its slope in the FeS-saturated system (Fig. 2B). With further crystallization, the release of H2O continues to promote de-sulfidation to the point where all available S is contained in the magmatic fluid phase (dashed lines “Po out,” “any out” in Fig. 2B). As a result, total S concentration in the fluid first increases with decreasing pressure but, after exhaustion of S minerals, decreases due to dilution by magmatic H2O (mol fraction XS,tot = XH2S + XSO2 indicated by scales of light to darker orange in Figure 2).Lowering the bulk FeIII/Fetot at constant H2O content leaves the fluid saturation pressure essentially unchanged except at high temperatures (1000 °C), where FeS de-sulfidation is suppressed (Fig. 3A, thick green line) due to the lower stability of SO2 relative to H2S (symbol size in Fig. 3B). For the same reason, final pyrrhotite disappearance shifts to lower pressures (Po out; dashed purple versus green lines in Fig. 3A). The SO2/H2S ratio in the fluid (Fig. 3B) relates to the redox state of the system as measured by buffer deviations; e.g., ΔlogfO2(QFM) (QFM—quartz-fayalitemagnetite). Varying bulk FeIII/Fetot from 0.2 to 0.5 increases ΔlogfO2(QFM) from +1.0 to +2.2 (see the Supplemental Material), which is reasonable in light of natural oxybarometers (Richards, 2015; Matjuschkin et al., 2016). Halving the H2O content from 6 wt% to 3 wt% shifts all curves to lower pressure because fluid saturation requires higher degrees of crystallization.We conclude that sulfides in hot arc magma can persist to the upper crust, where they decompose and transfer S to a hydrous fluid over a small P-T interval, well before the magma fully crystallizes (Figs. 2C and 2D). By contrast, along cooler geothermal gradients, the magma reaches fluid saturation at mid-crustal levels; the lower temperature and higher pressure inhibit sulfide decomposition, leading to the dispersal of S-poor aqueous fluid from intrusive rocks that retain their magmatic sulfide phase (Fig. 2A). Both arc-magma cases contrast with volatile-poor, and typically hotter, melt-rich flood basalts, in which minor hydro-carbonic fluid exsolves as a consequence of decompression, with the result that magmatic sulfide persists to near-surface pressures.Bubble nucleation in liquids is reduced by mineral surfaces, such that heterogeneous nucleation tends to occur on the mineral with the largest outer angle, Ψ, between mineral and vapor (Fig. 4A). In silicate magmas, typically Ψ is maximized by non-silicate minerals, magnetite, or sulfide (Fiege and Cichy, 2015). Composite fluid + sulfide inclusions in magnetite (Georgatou and Chiaradia, 2020) indicate larger Ψ of vapor against sulfide compared with vapor against magnetite, implying that bubble nucleation is most likely initiated on sulfide particles (Fig. 4A; Wang et al., 2020).The subsequent growth of a H-O-S–dominated fluid bubble is limited by the diffusion of H2O through the silicate melt, with H2O—which is known to diffuse rapidly—being the dominant volatile component in the magma and the reactant driving de-sulfidation (Reactions 2 and 3; Fig. 4B; Zhang and Ni, 2010). By contrast, the transfer of S, Fe, Cu, and other chalcophile metals from a decomposing sulfide particle to an attached fluid bubble requires no diffusive transport through the silicate melt. Therefore, the growing bubble will directly incorporate S and metals from the decomposing sulfide, and bulk metal extraction from magma carrying separate sulfide particles may be faster and more complete than from sulfide-undersaturated magma.If sulfide saturation does not result in sulfide loss, it causes no bulk Cu depletion and is not a limiting factor for ore formation (cf. Chiaradia, 2014; Chelle-Michou and Rottier, 2021). Our results show, to the contrary, that early magmatic sulfide saturation in arc magmas may be a first step in Cu enrichment, actively promoting later porphyry copper ore formation. Optimal conditions for sulfide entrainment and subsequent decomposition to ore-forming fluid match earlier observations of magmas enabling fertile ore provinces, including oxidizing conditions and high water content. Both processes are favored by the rapid ascent of hot, hydrous magmas toward Earth's surface from constrained magma reservoirs fractionating at the base of thickened crust in compressive tectonic settings (Sillitoe, 2010; Loucks, 2021). Our arguments extend the model of Lee and Tang (2020) for porphyry copper ore formation, but little or no Cu needs to be lost at the base of the crust, and no extreme redox conditions due to garnet removal are required.Physical transport of sulfides and their decomposition upon fluid saturation shifts the focus from chemical modeling of element distribution between sulfide, silicate melt, and fluid (e.g., Chen et al., 2020; Rottier et al., 2020; Chelle-Michou and Rottier, 2021) to the question of surface interaction between sulfide particles (solid or molten) and major minerals that are removed during fractional crystallization (Yao and Mungall, 2020). Net S and chalcophile metal depletion would occur by sulfides preferentially attached to major minerals. If sulfides form isolated globules in silicate melt, as available evidence suggests (Wang et al., 2020), the bulk magma may experience net sulfide enrichment so that Cu becomes transiently concentrated like an incompatible element (Cline and Bodnar, 1991) for subsequent transfer to the fluid phase. Such ore metal enrichment can result simply from the entrainment of sulfides with the fractionating silicate melt and does not require prior physical accumulation of sulfides. If re-mobilization of lower-crustal sulfide accumulations indeed adds to further enrichment (Core et al., 2006), as suggested by other researchers (e.g., Chiaradia, 2014; Du and Audétat, 2020), then physical mobilization by rapid magma extraction seems more likely than chemical mobilization, which would require a fundamental magma-chemical change from sulfide precipitation to sulfide re-dissolution. Added buoyancy by sulfide attachment to bubbles and the presence of molten sulfide may enhance enrichment in upper-crustal reservoirs (Mungall et al., 2015), but these conditions are not essential for avoiding metal loss.The fraction of Cu that can be physically transported to the upper crust depends on sulfide quantity. For 0.2–0.5 wt% FeS and assumed distribution coefficients of Cu or Ag between monosulfide solid solution and silicate melt (400 or 60, respectively; Li and Audétat, 2012), the sulfide phase can carry 45–66% of the initially available Cu to the upper crust (but <20% of initial Ag; see the Supplemental Material). This amount is comparable to the deficit of Cu in volcanic rocks above thick continental crust compared to arc rocks above thin crust (~70%; Chiaradia, 2014) and the Cu/Ag deficit in the bulk continental crust compared to primitive arc basalts (~50%; Chen et al., 2020). Selective depletion of the most chalcophile precious metals (Au, Pd, and Pt) by removal of a small amount of sulfide may explain the giant Cu-only deposits of Chile (Park et al., 2021). However, the low concentration of Pd and Pt in ore deposits is not a conclusive argument against sulfide entrainment and subsequent transfer to magmatic fluid: all these elements are highly soluble at magmatic temperatures (e.g., Sullivan et al., 2022) and their abundance in ore deposits therefore depends on selective precipitation efficiency. Future modeling may combine our approach with partitioning of elements between fluid, sulfide phases, and silicate melt, including dissolved S. Our first-order estimate suggests the possibility that some of the global deficit of chalcophile metals could be due to dispersion via magmatic fluids to the hydrosphere and recycling by sediment subduction (cf. Soyol-Erdene and Huh, 2012) rather than cumulate loss to the mantle alone.We thank Giada Iacono-Marziano, James Mungall, and Richard Sillitoe for critical reviews that helped clarifying our arguments and we appreciate Marc Norman's thoughtful editorial handling of this paper. Continued support by ETH Zürich and earlier funding by the Swiss National Science Foundation (Project 200020-166151) is acknowledged.

中文翻译：

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岩浆硫化物的物理运移促进热液矿液中铜的富集

岩浆硫化物流失到地幔被认为是解释演化弧岩浆铜缺乏和大陆地壳贫铜/银比的原因。我们解决了饱和硫化物是否可能被上升的岩浆机械夹带的问题，以及这将如何影响它们在上地壳中的地球化学命运。考虑到硫化物的润湿特性和相对于岩浆上升速度的沉降速度，夹带是合理的。夹带的硫化物使岩浆相对于上地壳中的 HOS 流体变得饱和的压力增加了 10-100 MPa，压力差随着温度、含水量和氧化的增加而增加。气泡很可能在硫化物颗粒上成核，允许 S 和 Cu 在一个小的结晶间隔内从硫化物转移到流体中，而不受通过硅酸盐熔体扩散的限制。这一系列过程使岩浆硫化物在矿石金属运输和富集形成斑岩铜矿床中发挥了积极作用，并可能对地壳铜预算产生全球影响。与普通岩石相比，斑岩铜矿床含有数百万吨的铜，其富集数量级. 这些极端异常是由从岩浆到流体再到矿石的几个富集步骤形成的（Sillitoe，2010）。相比之下，目前设想之前的演变是部分耗尽步骤，这是由硫化物饱和螯合最初存在于原生弧玄武岩中的亲矿金属引起的（例如，Chen 等人，2020 年）。厚大陆地壳上方的弧形火山岩和大块大陆地壳中铜的全球缺乏（Chiaradia，2014 年），再加上下地壳堆积物中常见的硫化物存在和部分铜富集（Métrich 等人，1999 年；Rezeau 和 Jagoutz，2020 年） )，据信表明通过再循环到地幔中铜和其他嗜铅金属会大量损失（Lee 等人，2012；Jenner，2017；Park 等人，2021）。矛盾的是，岩浆弧岩的铜亏缺在构造环境中最大，而这些构造环境也拥有世界上主要的斑岩铜矿区（Chiaradia，2014；Loucks，2021）。与斑岩铜矿相关的岩浆中广泛存在副硫化物，这表明下地壳中的硫化物饱和度对成矿无害（Du 和 Audétat，2020；Rottier 等，2020）。岩浆硫化物在斑岩铜矿床形成中的作用主要集中在上地壳过程；例如，瞬态嗜热元素储存、硫化物积累和再活化、复合颗粒的气泡浮选以及流体饱和时硫化物的大量或部分分解，这会影响所形成矿床的整体金/铜比（Hattori 和 Keith，2001 年；Halter等人，2004；Nadeau 等人，2010；Wilkinson，2013；Mungall 等人，2015；Yao 和 Mungall，2020）。相反，最近的研究集中在确定构造和岩浆条件，以最大限度地减少下地壳铜的损失，并优化从演化岩浆中剩余铜形成矿床的机会（Richards，2015 年；Lee 和 Tang，2020 年；Rezeau 和 Jagoutz，2020 年；Chelle -Michou 和 Rottier，2021 年；Park 等人，2021 年）。我们质疑普遍认为下地壳硫化物饱和必然意味着硫化物损失和随之而来的岩浆金属耗竭的观点。我们探索了另一种可能性，即岩浆硫化物的初始富集之后是由上升的硅酸盐熔体机械夹带硫化物颗粒（Core et al., 2006），并量化其对上地壳岩浆流体饱和度和嗜铬金属转移的影响测量地幔矿物与富含 FeS 的硫化物熔体之间的二面角的实验表明，硫化物与硅酸盐颗粒表面接触的润湿特性有利于硅酸盐熔体中的孤立硫化物球体（Wang 等，2020）。单硫化物固溶体颗粒通常与更多富含铜和镍的硫化物熔体形成复合球体，没有表现出优先附着于主要氧化物和硅酸盐的趋势（例如，Li 和 Audétat，2012 年）。硫化物颗粒或液滴是否沉降或夹带在熔体由硫化物的下沉速度相对于主体硅酸盐岩浆的上升速度决定（Tomkins 和 Mavrogenes，2003 年）。硫化物和硅酸盐熔体之间的密度差 Δr 线性进入 Stokes 公式，而粒子半径 r 按其平方进入硅酸盐熔体粘度 μ：对等式 1 的评估（参见补充材料 1）表明，主要成分对粘度的影响——二氧化硅和水含量——部分抵消，因此，玄武岩的外推曲线近似于在较低温度下具有较高水含量的更多分馏熔体（图 1）。在岩浆玻璃和斑晶中观察到的硫化物颗粒尺寸通常为 1-100 μm（Halter 等人，2004 年；Du 和 Audétat，2020 年；Georgatou 和 Chiaradia，2020 年），硫化物颗粒通过扩散和聚结生长的模型表示上限约为 300 μm（Yao 和 Mungall，2020）。 U-Th 系列不平衡的上升速度基于地幔源和地表之间的转移持续时间，包括储存期，因此代表最小流速（Turner 和科斯塔，2007）。当流体饱和引发火山喷发时，基于扩散的速度计对下地壳上升和上地壳更快的速度产生了类似的估计（Neave 和 Maclennan，2020 年）。比较（图 1，灰色条）表明，未被包含在堆积晶体中的硫化物通常可以通过硅酸盐熔体运输。Lesne 等人。（2015）表明，溶解在硅酸盐岩浆中的硫增加了岩浆流体饱和的压力和深度，但他们没有考虑单独硫化物相的饱和度，这是我们分析的重点。我们探讨了磁黄铁矿、硬石膏和 HOS 流体相与可变结晶岩浆平衡的相对稳定性。富含 Fe-S 的单硫化物固溶体（简化为非化学计量的 FeS）的稳定性和分解是通过将气体物质的分压与共存的硅酸盐熔体中的 H2O(m) 和 FeO(m) 联系起来的反应来控制的。在还原条件下，主要的 S-II 物质形成为 (Mungall et al., 2015)：在氧化条件下，S+IVO2 形成为：其中 H2O(m) 控制主要流体物质 H2O(g) 和 O2 逸度(fO2) 由 H2O(g) = 0.5O2(g) + H2(g) 控制。中间价 S2(g) 和 H2(g) 是次要的气体种类，后者受 H2(g) + Fe2O3(m) 2 FeO(m) + H2O(m) 的限制。我们通过吉布斯能量最小化评估了这些反应使用 Holland 等人的解决方案模型。（2018 年）。与早期的熔体-硫化物-流体平衡模型相比（参见 Mungall 等人，2015 年），岩浆中成岩矿物的含量与硫化物和流体的含量同时变化。与 Yao 和 Mungall (2020) 的模型化学相比，模型化学得到了简化，因为忽略了 Cl 和 C，S 在熔体中的溶解度（压力 [P]、温度 [T] 和熔体成分的函数，尤其是氧化还原条件；例如，Matjuschkin 等人，2016）。我们忽略 C，因为它为模型增加了任意程度的自由度；对可能的熔体 CO2 含量的计算表明，虽然 CO2 可能在较高压力下导致流体饱和，但流体的量非常小，以至于它对脱硫只有二阶后果（补充材料中的图 S1）。我们的方法得到了简化，但强调了结晶对于水性流体生产的一级结果作为一种自我增强的过程，因为熔体中的 H2O 损失反过来促进了结晶。我们选择了 Rezeau 和 Jagoutz (2020) 的含水弧玄武岩成分，与 Chiaradia (2014) 和其他人使用的相似，它们应用了替代熔体模型。闪石已被排除在外，因为这种解决方案模型令人难以置信地抑制了磁铁矿的稳定性，因此辉石在我们的模型系统中取代了镁铁质矿物（参见补充材料）。我们展示了固定块状成分的结果，而不是分级结晶的冷却路径，以说明岩浆硫化物在 PT 区域的影响（图 2）。为了引入 S，将 0.5 wt% FeS 添加到模型玄武岩组合物中。与硫化物饱和时的 S 溶解度（Chelle-Michou 和 Rottier，2021 年）以及硫化物饱和镁铁质弧火山岩中硫化物丰度的岩相学估计值（Métrich et al., 1999; Larocque et al., 2000)。矿物，在中地壳压力下，+石榴石±长石让位于富含磁铁矿的尖晶石+长石。减压导致流体饱和（图 2B 中的紫色实线曲线），其压力因硫的存在而增加。这种增加的幅度，ΔP(S)，通过在不添加 FeS 的情况下平衡相同的体积组成来获得（图 2B 中的紫色点状曲线）。ΔP(S)随着温度的升高而增加，这促进了反应（2）和（3）的脱硫，因此在~1000°C以上，流体饱和曲线在FeS饱和系统中反转其斜率（图2B） . 随着进一步结晶，H2O 的释放继续促进脱硫，直至所有可用的 S 都包含在岩浆流体相中（图 2B 中的虚线“Po out”、“any out”）。因此，流体中的总 S 浓度首先随着压力的降低而增加，但在 S 矿物质耗尽后，由于岩浆 H2O 的稀释而降低（摩尔分数 XS，tot = XH2S + XSO2，如图中从浅橙色到深橙色的刻度所示2）。在恒定 H2O 含量下降低体积 FeIII/Fetot 使流体饱和压力基本不变，除非在高温（1000 °C）下，由于 SO2 的稳定性较低，FeS 脱硫受到抑制（图 3A，粗绿线）相对于 H2S（图 3B 中的符号大小）。出于同样的原因，最终磁黄铁矿的消失转移到较低的压力（Po out；图 3A 中的紫色虚线与绿线）。流体中的 SO2/H2S 比率（图 3B）与系统的氧化还原状态有关，通过缓冲偏差测量；例如，ΔlogfO2(QFM)（QFM-石英-铁橄榄石磁铁矿）。将体积 FeIII/Fetot 从 0.2 变化到 0.5 将 ΔlogfO2(QFM) 从 +1.0 增加到 +2.2（参见补充材料），根据天然氧气压计，这是合理的（Richards，2015；Matjuschkin 等人，2016）。将 H2O 含量从 6 wt% 减半至 3 wt% 会使所有曲线向较低压力移动，因为流体饱和需要更高程度的结晶。我们得出结论，热弧岩浆中的硫化物可以持续存在于上地壳，在那里它们分解并将 S 转移到在一个小的 PT 间隔内，远在岩浆完全结晶之前的含水流体（图 2C 和 2D）。相比之下，沿着较冷的地热梯度，岩浆在地壳中部达到流体饱和；较低的温度和较高的压力会抑制硫化物分解，导致 S 贫含水流体从保留其岩浆硫化物相的侵入岩中扩散（图 2A）。两种弧形岩浆情况都与挥发性较差、通常较热、富含熔体的溢流玄武岩形成对比，其中少量烃类流体由于减压而溶出，结果岩浆硫化物持续存在于近地表压力。液体中的气泡成核被矿物表面减少，因此异质成核倾向于发生在矿物和蒸汽之间具有最大外角Ψ的矿物上（图4A） . 在硅酸盐岩浆中，通常 Ψ 因非硅酸盐矿物、磁铁矿或硫化物而最大化（Fiege 和 Cichy，2015 年）。磁铁矿中的复合流体 + 硫化物包裹体（Georgatou 和 Chiaradia，2020 年）表明蒸汽对硫化物的 Ψ 大于蒸汽对磁铁矿的 Ψ，这意味着气泡成核最有可能在硫化物颗粒上引发（图 4A；Wang 等人，2020） .HOS 为主的流体气泡的后续生长受到 H2O 通过硅酸盐熔体扩散的限制，H2O（已知会迅速扩散）是岩浆中的主要挥发性成分，也是驱动脱硫的反应物（反应 2 和 3；图 4B；Zhang 和 Ni，2010）。相比之下，S、Fe、Cu 和其他嗜硫金属从分解的硫化物颗粒转移到附着的流体气泡不需要通过硅酸盐熔体的扩散传输。因此，生长的气泡将直接吸收分解硫化物中的硫和金属，从携带单独硫化物颗粒的岩浆中提取大块金属可能比从硫化物欠饱和岩浆中提取更快、更完整。如果硫化物饱和不会导致硫化物损失，它不会导致大量铜消耗，也不是矿石形成的限制因素（参见 Chiaradia，2014；Chelle-Michou 和 Rottier，2021）。我们的结果表明，相反，认为弧形岩浆中早期岩浆硫化物饱和可能是Cu富集的第一步，积极促进后期斑岩铜矿的形成。硫化物夹带和随后分解成成矿流体的最佳条件与早期对岩浆的观察相匹配，这些岩浆使矿区肥沃，包括氧化条件和高含水量。在压缩构造环境中，在加厚地壳底部分馏的受限岩浆储层向地球表面快速上升的热含水岩浆有利于这两种过程（Sillitoe，2010；Loucks，2021）。我们的论点扩展了 Lee 和 Tang (2020) 的斑岩铜矿形成模型，但在地壳底部几乎不需要损失铜，也不需要由于石榴石去除而导致的极端氧化还原条件。硫化物的物理传输及其在流体饱和时的分解将焦点从硫化物、硅酸盐熔体和流体之间元素分布的化学建模转移（例如，Chen 等人，2020；Rottier 等人，2020；Chelle-Michou 和 Rottier， 2021 年）关于硫化物颗粒（固体或熔融）与在分级结晶过程中去除的主要矿物之间的表面相互作用问题（Yao 和 Mungall，2020 年）。硫化物优先附着在主要矿物上，会导致净 S 和嗜硫金属耗尽。如果硫化物在硅酸盐熔体中形成孤立的小球，如现有证据所示（Wang 等人，2020 年），大块岩浆可能会经历硫化物净富集，从而使铜像不相容的元素一样短暂浓缩（Cline 和 Bodnar，1991 年），以便随后转移到液相。这种矿石金属富集可以简单地由分馏硅酸盐熔体夹带硫化物引起，并且不需要硫化物的预先物理积累。如果像其他研究人员（例如，Chiaradia，2014；Du 和 Audétat，2020）所建议的那样，下地壳硫化物聚集物的重新流动确实增加了进一步的富集（Core 等，2006），那么通过快速岩浆提取进行物理流动似乎比化学动员更有可能，这需要从硫化物沉淀到硫化物再溶解的基本岩浆化学变化。硫化物附着在气泡上增加浮力和熔融硫化物的存在可能会增强上地壳储层的富集（Mungall 等，2015），但这些条件对于避免金属损失并不是必需的。可以物理输送到上地壳的铜的比例取决于硫化物的数量。对于 0.2-0.5 wt% FeS 和假设的单硫化物固溶体和硅酸盐熔体之间的 Cu 或 Ag 分布系数（分别为 400 或 60；Li 和 Audétat，2012），硫化物相可以携带 45-66% 的初始可用 Cu到上地壳（但 <20% 的初始 Ag；参见补充材料）。这一数量与厚大陆地壳上方火山岩中与薄地壳上方弧岩相比的铜缺乏量相当（~70%；Chiaradia，2014）和与原始弧玄武岩相比，大块大陆地壳中的铜/银缺乏量（~ 50%；陈等人，2020）。选择性消耗最亲热的贵金属（Au、Pd、和 Pt）通过去除少量硫化物可以解释智利巨大的纯铜矿床（Park 等人，2021 年）。然而，矿床中 Pd 和 Pt 的低浓度并不是反对硫化物夹带和随后转移到岩浆流体中的决定性论据：所有这些元素在岩浆温度下都高度可溶（例如，Sullivan 等人，2022 年）并且它们在因此，矿床取决于选择性沉淀效率。未来的建模可能会将我们的方法与流体、硫化物相和硅酸盐熔体（包括溶解的 S）之间的元素分配相结合。我们的一阶估计表明，全球某些嗜铬金属的短缺可能是由于岩浆流体分散到水圈和沉积物俯冲循环（参见 Soyol-Erdene 和 Huh，2012 年），而不是单独累积地幔损失。我们感谢 Giada Iacono-Marziano、James Mungall 和 Richard Sillitoe 的批评性评论，帮助澄清了我们的论点，我们感谢 Marc Norman 对本文的周到的编辑处理。承认苏黎世联邦理工学院的持续支持和瑞士国家科学基金会（项目 200020-166151）的早期资助。